Nihilism is the philosophical position which argues that Being, especially past and current human existence, is without objective meaning, purpose, comprehensible truth, or essential value. It asserts that there is no reasonable proof of the existence of a higher ruler or creator, that a "true morality" does not exist, and that objective secular ethics are impossible. Therefore life has, in a sense, no truth and no action is objectively preferable to any other.

The term "nihilism" was first popularized by the novelist Ivan Turgenev (1818 - 1883). Art movements such as Dada and Futurism, and philosophical movements like Existentialism, Post-Modernism, Post-Structuralism and Deconstructionism have all been identified by commentators as "nihilistic" at various times in various contexts. Nihilism differs from Skepticism in that Skepticism does not reject claims to truth outright, it only rejects these claims if there is insufficient empirical evidence to support them.

Nihilism is most often associated with the German philosopher Friedrich Nietzsche, although he never actually advocated Nihilism as a practical mode of living and was typically quite critical of it. He was, however, one of the first philosophers to study nihilism extensively. Nietzsche's criticism of nihilism was mainly on that grounds that it can become a false belief, and lead individuals to discard any hope of meaning in the world and thus to invent some compensatory alternative measure of significance. He also asserts that Nihilism is a result of valuing "higher", "divine" or "meta-physical" things (such as God), that do not in turn value "base", "human" or "earthly" things, and that any form of Idealism, after being rejected by the idealist, leads to Nihilism. According to Nietzsche, it is only once nihilism is overcome that a culture can have a true foundation upon which to thrive.

Similarly, Jacques Derrida, whose Deconstructionism movement is commonly labelled nihilistic, did not himself make the claims often attributed to him. In fact, Deconstructionism can be seen not as a denial of truth, but as a denial of our ability to know truth (i.e. it makes an epistemological claim as opposed to Nihilism's ontological or metaphysical claim).

• Metaphysical Nihilism (or Blob Theory):
  This is the theory that there are no objects or that objects do not exist, and therefore empirical reality is an illusion, or, more commonly, the theory that there might have been no objects at all (i.e. that there is a possible world in which there are no objects at all). An object, here, is a thing, an entity or a being that can have properties and bear relations to other objects. This position has been variously attributed to philosophers such as Parmenides, Buddha, Hindu Advaita Vedantins and Immanuel Kant.
• Mereological Nihilism (or Compositional Nihilism):
  This is the position that objects with proper parts do not exist, (and, by corollory, objects existing in time do not have any temporal parts), and only basic building blocks (e.g. electrons, quarks) exist. (Mereology is the theory of the relations of part to whole, and the relations of part to part within a whole). These smallest building blocks are individual and separate items that do not ever unify or come together into being non-individual. If the building blocks of reality never compose any whole items, then all of reality does not involve any whole items, even though we may think it does. Thus, the world we see and experience, which appears to be full of objects with parts, is a product of human misperception. One philosopher who has argued for something close to pure mereological nihilism is Peter Unger, in his papers "There Are No Ordinary Things" and "I Do Not Exist".
• Partial Nihilism:
  Some philosophers argue that only objects of a certain kind have parts. One such position is Organicism, the view that living beings are composites (i.e. objects that have parts) and therefore exist, but there are no other objects with parts, and all other objects that we believe to be composite (e.g. chairs, planets, etc) therefore do not exist. However, Organicists such as Peter van Inwagen assert that, even if there is no such things as a table, there are simples (basic building blocks) "arranged table-wise".
• Moral Nihilism is the meta-ethical view that ethical claims are generally false. It holds that there are no objective moral facts or true propositions - that nothing is morally good, bad, wrong, right, etc - because there are no moral truths (e.g. a moral nihilist would say that murder is not wrong, but neither is it right). The philosophy of Niccolò Machiavelli is sometimes presented as a model of Moral Nihilism, but that is highly questionable as he was largely silent on moral matters and, if anything, he presented an alternative to the ethical theories of his day, rather than an all-out rejection of all morality.